What happened
While on final approach, approximately 15 feet above a rooftop helipad, the helicopter controls became very stiff. During this period, the pilot noted that the "HYD" light on the caution panel was illuminated, though the audible hydraulic warning horn failed to activate. The aircraft subsequently struck the helipad with its right skid and rolled onto its right side.
The investigation
Investigators examined the cockpit and discovered that the hydraulic cut-off switch, located on the collective control, was in the cut-off position. The red plastic guard for this switch was found to be broken. While the cockpit was searched for fragments of the broken guard, no pieces were located.
An inspection of the hydraulic system showed no leaks. Additionally, a functional test performed on both the hydraulic pump and the regulator/manifold revealed no anomalies in either unit.